Extracorporeal blood treatment and system having reversible blood pumps

ABSTRACT

An extracorporeal blood processing method using a blood circuit comprising a pair of blood passages attached to opposite flow ends of a blood treatment device and said blood circuit is mounted on a blood pump console, the method includes: withdrawing blood from a vascular system of a human patient and drawing the blood into the blood circuit; pumping the withdrawn blood through one of the pair of blood passages using a first blood pump of the console and into the blood treatment device; pumping the treated blood from the treatment device through the other of the pair of blood passages using a second blood pump of the console; infusing the treated blood from the other blood passage and into the vascular system of the patient, and periodically reversing a flow direction of blood through the pair of blood passages and blood treatment device.

RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/002,442, (U.S. Pat. No. 7,615,028) filed on Dec. 3, 2004, theentirety of which is incorporated by reference.

FIELD OF INVENTION

The present invention relates to the field of extracorporeal bloodtreatment systems. In particular, the invention relates to reversibleperistaltic pumps for a portable extracorporeal treatment device.

BACKGROUND OF THE INVENTION

Congestive Heart Failure (CHF) is a form of heart disease stillincreasing in frequency. According to the American Heart Association,CHF is the “Disease of the Next Millennium”. The number of patients withCHF is expected to grow even more significantly as an increasing numberof the “Baby Boomers” reach 50 years of age.

CHF is a condition that occurs when the heart becomes damaged andreduces blood flow to the organs of the body. If blood flow decreasessufficiently, kidney function becomes impaired and results in fluidretention, abnormal hormone secretions and increased constriction ofblood vessels. These results increase the workload of the heart andfurther decrease the heart's pumping ability and, in turn, causesfurther reductions in blood flow to the kidney. It is believed that theprogressively-decreasing perfusion of the kidney is a principalnon-cardiac cause perpetuating the downward spiral of the “Vicious Cycleof CHF”. Moreover, the fluid overload and associated clinical symptomsresulting from these physiologic changes are a predominant cause forexcessive hospital admissions, poor quality of life and large costs tothe health care system due to CHF.

There is a long-felt demand for a miniature and portable extracorporealfluid treatment devices for patients suffering from repeated fluidoverload. Such a device might be worn during the day as the patientmoves about. The device would preferably be easy to use. If theprocedure for inserting catheters percutaneously is too complicated, itwill be difficult to have sufficiently trained clinical personnelavailable to insert the catheter. Standard OTN (Over The Needle)catheters generally require nurses with intravenous (IV) insertionexperience to insert catheters to gain blood access for the fluidremoval device. When midline catheters are used for accessing bloodperipherally, the insertion of the catheter is limited to clinicianswith the required training. To insert PICC (Peripherally InsertedCentral Catheter) line requires IV nurses with training in seldingerinsertion technique and doctors with similar training.

Utilizing an ultrafiltration fluid removal device that uses standard IVaccess would greatly simplify the process. A simpler approach would beto use an implanted port whereby the nurse could quickly gain access toblood flow. Implanted ports are commonly used for drug infusiontherapies and are ideal for long term access. Implanted ports are alsoaccessed via IV needles. Ports have reduced infection rates whencompared with standard central venous percutaneous catheters and areideal for repeatable access over long periods of time.

Peripheral IV blood access is not without its own inherent issues, whichinclude: (1) The blood flow may be limited and intermittent withperipheral access because the further down the peripheral vein treeblood flow is accessed there is less blood flow is available and themore that the available blood flow is subject to fluctuations in flow.Implanted ports can overcome many of these limitations because they areplaced centrally. (2) The majority of nurses are comfortable using OTNswith sizes of 20 G and less. These are simpler to insert, cause lesstrauma and facilitate multiple insertions. If larger catheters gaugesizes are required, the percentage of nurses that can gain accesswithout trouble quickly diminishes which would cause a further hurdle tothe usage of such an ultrafiltration device. However, the smaller thegauge size of the catheter the smaller its internal diameter whichresults in a limitation in the maximum blood flow that can be achieved.This limitation is due to the maximum positive and negative pressuresthat blood can safely be exposed to without compromising patient safety.Patients with fluid overload also suffer from peripheral edema and theedema tends to hide the veins by placing them further from the skinsurface making it more difficult to locate them. In these cases theclinician resorts to multiple sticks before a vein is located. Thesmaller the IV catheter the more acceptable such a procedure is. Largergauge needles increase the trauma to the arm and are less acceptable topatients. Implanted ports will overcome many of these limitationsbecause access is gained via a septum which when located makes gainblood flow access relatively simple.

When low blood flow is used in an extracorporeal device, it creates asignificant engineering challenge. In general the lower the blood flow,the longer the residence time of blood extracorporeally and the greaterthe propensity of the device to clot. Lower blood flows increases thedifficulty of pressure sensors to reliably detect infusion disconnects.Lower blood flows yield lower pressure drops that result in a largepressure sensor signal to noise ratio between the pressure dropattributed to the access and variations in pressure due to patientmovement. When peripheral vein access is used or when a patient istreated for an extended period of time, it is normal to expect thepatient to be mobile and that the patient will move about, bend over andlift their arms to stretch occasionally during treatment. Everycentimeter (cm) in height change of the patient's arm having thewithdrawal and/or infusion catheter results in a 0.75 mmHg pressureincrease or decrease in the blood circuit due to the resultant change instatic head pressure. Accordingly, the ratio between variation in statichead pressure due to patient movement and needle pressure drop due toblood flow should be relatively insignificant so that false alarms willnot be annunciated. Disconnection of blood tubes/access in the circuitare generally detected by a reduction in the pressure drop across aneedle. It may be hard to distinguish pressure fluctuations due topatient motion and to needle disconnects. It is accepted medically thata blood loss of 100 ml or less will not result in the patients' healthbeing compromised. In the case of the typical dialysis machine this timeperiod is 100 ml/400 ml/min or 15 seconds. Disconnection algorithms haveto be extremely sensitive to ensure patient safety. In hemodialysisstandards, such as IEC 60601-2-16, the standards committee was awarethat there are inherent limitations in using pressure measurements fordetecting disconnects which is why devices which use high blood flowshave been limited to ICU and dialysis clinic use up until recently. Itis also recognized as being an increased risk for the use of homedialysis.

SUMMARY OF INVENTION

A novel extracorporeal blood treatment system is proposed that takesadvantage of the low blood flow while achieving a medically significantvolume of ultrafiltrate removal and device portability.

It is medically accepted that a blood loss of 100 ml or less will notresult in the patients' health being compromised. In the USA, MDR(Medical Device Report) are typically filled out if a blood loss of over100 ml occurs. In the performance dialysis a blood loss of more than 100ml may occur in less than 15 seconds. Thus disconnection algorithms haveto be extremely sensitive and quick for blood circuits having highvolume blood flow, such as in dialysis machine.

With high blood flow, disconnects of blood lines in extracorporealdevices must be detected as soon as possible. Without quick detection ofdisconnections, the patient could bleed to death in a relatively shortperiod of time. A lower blood flow device allows for a longer detectiontime while maintaining safety before blood loss becomes detrimental tothe patient. The lower the blood flow the longer the time which may beallowed to determine that a blood loss is occurring.

The blood circuit may be symmetrical which facilitates ultrafiltrationwhen the blood pumps are rotating clockwise or counterclockwise. A firstblood pump withdraws blood into a withdrawal tube of the blood circuit.A second blood pump draws blood from a filter and infuses the blood intothe vascular system of the patient. A third pump draws filtrate from thefilter and controls the rate of filtrate flow to a filtrate collectionbag. The withdrawal and infusion tubes of the circuits may be connectedto an implanted blood port(s) under the skin of the patient orperipheral IV needles inserted into peripheral veins.

In one embodiment, a portable ultrafiltration system is proposed that iscapable of removing at least 1 liter of filtrate fluid every 24 hrs, andoperating on battery for at least 8 hrs. The disposable circuitcomponent of the system is inexpensive and robust so as to undergo thechallenges of ambulatory care. The circuit may be able to operate for 24hrs. or more before replacement with a new circuit. A pump controller ofthe system regulates the flow rate of blood through the circuit. Theblood flow may be set by the controller in a range of 5 to 15 ml/min.The controller may adjust the maximum blood flow setting in, forexample, increments of 1 ml/min based upon the physiological blood flowpresent.

The withdrawal and infusion tubes of the circuit both pass through anair detector(s) before connection to the patient. The air detector senseair bubbles in the blood tubes to detect disconnections in the bloodtube. Disconnection occurring downstream of the air detectors are notsensed by the air detectors until the blood flow is reversed. When thepumps reversed the blood flow, air drawn in through the disconnection orleak is sensed as the air bubbles flow past the air detector. Reversalof the blood flow ensures that disconnections and leaks in the bloodcircuit are sensed by the air detectors.

The blood flow is reversed at a cyclical rate to prevent a large volumeof blood from being discharged from a leak or disconnection. Thereversal cycle period is determined by the pump controller as a functionof the set blood flow rates. Reversals are set to occur frequently orperiodically such that blood loss due to disconnect never exceeds 100ml. For example, when the blood flow is set to 5 ml/min the blood pumpis reversed in direction every 20 minutes. During a first twenty minuteperiod of operation both blood pumps are rotate clockwise. At the end ofthe first period, the pumps both reverse to rotate counterclockwise andthereby reverse the flow direction of blood through the circuit. At theend of the second twenty minute period, the cycle repeats. If adisconnect were to occur during operation, at 5 ml/min and a 20 minutecycle, a maximum of 100 ml is withdrawn from the patient and potentiallylost.

Alternatively, if the blood flow is set to 15 ml/min the period in timebetween pump reversals is reduced to 6.66 minutes because 15 ml/min×6.66min=100 ml. Reversal times for flow rates between 5 and 15 ml/min can becalculated from the simple equation: Reversal time (min)=100 (ml)/flowrate (ml/min). A safety factor, or allowance, could be subtracted fromthe reversal time to account for possible blood loss through the accesssites due to venous pressure.

Reversing the blood flow ensures that the occurrence of a circuitdisconnection is detected within two periods of the pump rotation cycle.If a disconnection or leak were present in the circuit, air would beentrained in the blood tube. The ultrafiltration device detects thepresence of the leak in either the clockwise or anticlockwise cycleblood withdrawal cycle. Blood loss will not exceed 100 ml or other suchpreset volume because the presence of a leak will be detected as soon asthe leak is under negative pressure and air is entrained and pumped pastthe air detector. The circuit blood volume is less than 5 ml. This lowvolume ensures the blood is outside the body a minimal amount of timeand reduces the chances of blood clotting within the circuit. Thecircuit blood volume includes any possible extensions and accessdevices.

The periodic reversals of the blood pumps have a number of otheradvantages including: the reversals of the blood flow reduces thepolarization layer of protein deposited upon the filter membrane (muchlike the static charge on a comb can be reduced by reversing thedirection that the comb is being rubbed); and proteins and white bloodcells which aggregate in the header of the filter which do not passthrough the filter are returned to the patient before they result in theformation of a clot.

Once a reversal in blood pump direction is initiated, the removal offiltrate from the filter is temporarily stopped for the duration of timeit takes for the blood in the filter and circuit to pass back throughthe filter. Stopping the filtrate pump during this period avoidsfiltering the blood twice. Double filtration of the same volume of bloodwould increase the propensity of the filter to clot. The ultrafiltrationcessation time is a function of the volume of blood between the filterand the patient. For example, if the blood volume between the filter andpatient is 1 ml in the infusion line and the blood flow rate is 5ml/min, the ultrafiltration cessation period should be 12 seconds (1ml/5 ml/min) or greater. It may also be necessary to clear the volume ofblood in the blood access device, e.g. implanted port, before resumingfiltration. If the access being used is an implanted port with a bloodvolume of 3 ml then it will be beneficial to allow this volume of bloodto also be displaced back into the blood stream before reinitiatingultrafiltration.

Three pumps have a number of advantages including: it is possible tokeep the pressure in the filter positive or negative at all times bycontrolling the rate of the two blood pumps with respect to the rate ofultrafiltration which has the advantage of obviating the need formeasuring negative pressure or for detecting the presence of a leak;redefining significant pressure delays between the withdrawal pressurebeing sensed and the withdrawal catheter and the infusion pressure beingsensed and the infusion catheter which has the advantage of less dampingand signal delays of the pressure being measured facilitating a higherbandwidth control; simultaneously controlling withdrawal, infusion andfilter pressures; and it is no longer necessary to use a weight scalefor the filtrate collection bag because filter pressures will becomeexcessively high or low if the difference between the two blood pumpflow rates do not closely match the ultrafiltrate pump flow rate. Thusit is possible to continuously reference and check the flow of each pumpagainst each other.

One of the engineering challenges in developing a portable system is tolimit the power requirements of the device which in turn will minimizethe weight of the battery and the size of the overall device. Thisportable system uses novel power management systems in conjunction withhighly efficient motors to minimize the power consumption to less than10 watts. This enables portable therapy operation for up to 12 hourswith a battery weight of less than 1.5 lb battery. Such animplementation makes it feasible to produce a very reliable low flowportable ultrafiltration device minimizing the costs of the disposabledevice by simplifying its design while mitigating all known hazards in asafe and effective manner.

The invention may be embodied as an extracorporeal blood treatmentsystem comprising: a blood circuit comprising a first blood passagecoupled at a first end to a first end of a blood treatment device and asecond blood passage coupled at a first end to a second end of thetreatment device, wherein said first and second blood passages each havea second end adapted to be coupled to a vascular system of a humanpatient; a first blood pump connectable to the first blood passage and asecond blood pump connectable to the second blood passage, wherein saidfirst and second blood pumps are adapted to move blood through the firstand second blood passages in a first direction and in a reversedirection, and a pump controller operatively connected to the first andsecond blood pumps, said controller operates the blood pumps tocyclically move blood through the first and second blood passages in thefirst direction and the reverse direction.

The invention may be embodied as An extracorporeal blood processingmethod using a blood circuit comprising a pair of blood passagesattached to opposite flow ends of a blood treatment device and saidblood circuit is mounted on a blood pump console, said methodcomprising: withdrawing blood from a vascular system of a human patientand drawing the blood into the blood circuit; pumping the withdrawnblood through one of the pair of blood passages using a first blood pumpof the console and into the blood treatment device; pumping the treatedblood from the treatment device through the other of the pair of bloodpassages using a second blood pump of the console; infusing the treatedblood from the other blood passage and into the vascular system of thepatient, and periodically reversing a flow direction of blood throughthe pair of blood passages and blood treatment device.

Further the invention may be a method of extracorporeal blood processingmethod using a blood circuit comprising a pair of blood passagesattached to opposite flow ends of a blood treatment device and saidblood circuit is mounted on a blood pump console, said methodcomprising: withdrawing blood from a vascular system of a human patientand drawing the blood into the blood circuit; pumping the withdrawnblood through one of the pair of blood passages using a first blood pumpof the console and into the blood treatment device; pumping the treatedblood from the treatment device through the other of the pair of bloodpassages using a second blood pump of the console; infusing the treatedblood from the other blood passage and into the vascular system of thepatient; periodically reversing a flow direction of blood through thepair of blood passages and blood treatment device, and sensing apressure in the blood passage downstream of the blood treatment deviceduring both flow directions, and controlling a pumping rate of bloodthrough the downstream blood passages based on the pressure in thedownstream blood passage.

The invention may be further embodied as a method for monitoring avolume of filtrate in a collection bag comprising: placing thecollection bag in a walled container having a displaceable surface;filtering filtrate from extracorporeal blood flowing through a bloodcircuit; filling the collection bag with the filtrate; as the collectionbag fills with filtrate, the bag expands and displaces displaceablesurface; sensing a degree of displacement of the displaceable surface,and ceasing filling the collection bag with filtrate when the degree ofdisplacement exceeds a threshold value.

The invention may be embodied as a filtrate collection container systemcomprising: a container having at least one wall to receive thecollection container; a displaceable wall of said container abutting thecollection container; a bias applied to dispose the displaceable wallagainst the collection container, and a sensor detecting a force appliedby the collection container against the displaceable wall.

The invention may also be embodied as a method of collecting filtrate ina filtration bag of an extracorporeal blood circuit having a bloodfilter, said method comprising: withdrawing blood from a mammalianpatient into the blood circuit and filtering the blood with the filter;withdrawing filtrate from the filter and collecting the filtrate in anexpandable container; sensing an expansion of the container as filtrateis collected in the container, and determining the container is filledwith filtrate based on the expansion of the container.

The invention may be embodied as an extracorporeal blood treatmentsystem comprising: a blood circuit comprising a first blood passagecoupled at a first end to a blood filter and a second blood passagecoupled at a first end to the blood filter, wherein said first andsecond blood passages each have a second end adapted to be coupled to avascular system of a human patient; a first blood pump connectable tothe first blood passage and a second blood pump connectable to thesecond blood passage, wherein said first and second blood pumps areadapted to move blood through the first and second blood passages in afirst direction and in a reverse direction, and a filtrate pumpwithdrawing filtrate from the filter, and a pump controller operativelyconnected to the first and second blood pumps and to said filtrate pump.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an ultrafiltration system.

FIG. 2 is a schematic view of an ultrafiltration system with heparininfusion.

FIG. 3 illustrates of portable ultrafiltration device attached to apatient.

FIG. 4 is a diagram of lever arm pressure sensor.

FIG. 5 is a diagram of the electrical architecture of the control systemfor the ultrafiltration system.

FIG. 6 is a flow chart of the pressure control algorithm includingfeedback sensors and actuators under various occlusion conditions.

FIG. 7 is a flow chart of the Proportional Integral (PI) pressurecontrol algorithm.

FIGS. 8 a to 8 k show diagrams of the air detector and tubingconfiguration.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 shows a schematic of the ultrafiltration system 100. Withdrawalaccess 112 and infusion access 118 are obtained to and from the vascularsystem of the patient 110. Peripheral access via standard IV accessmethods is acceptable for use with this device. This is an advantage ofthe device described herein, but not a limiting requirement. The devicewill function just as effectively with other higher flow access methodssuch as a fistula, central venous catheter, implanted port, midline orPICC.

If required, withdrawal extension 114 connects proximally to withdrawalaccess via connectors 113, and distally to withdrawal tubing 130 viaconnectors 116. If required, infusion extension 120 connects proximallyto infusion access via connectors 119, and distally to infusion tubing132 via connectors 122. If extensions 114, 120 are not required, thewithdrawal tubing may connect directly to withdrawal access and infusiontubing directly to infusion access. The extensions are optional and usedfor making connections and extending circuit tube lines if needed. Amaximum blood volume of the extension may be specified to ensure thatthe maximum circuit volume is within a maximum volume so that leakdetection occurs without excessive loss of blood and to avoid anexcessive residence time of blood in the extracorporeal circuit.

Withdrawal tubing 130 and infusion tubing 132 both pass through or inproximity of air detector 134, such that air bubbles can be detected ineither tubing line. Alternatively two separate air detectors 134 may beutilized. The air detector 134 uses ultrasound to determine the presenceof air. An emitter and receiver of the air detector are placed on eithersides of the tubing and correctly acoustically coupled the signaltransmitted between emitter and receiver and through the blood tubing.Acoustic coupling requires that a liquid be present in the tubingbetween the emitter and receiver. Air attenuates the signalsignificantly and prevents the transmission of the ultrasonic pulsesthus enabling the detection of air.

Five different pressure sensors are employed in the described system100. These are pressure sensors 140, 144, 160, 164 and 170. Pressuresensors may be of the direct contact type and part of the disposablecircuit, or of the indirect contact type and part of the controllingsystem of the pump console. Sensors need not be the same type for eachlocation.

After passing through the air detector, the withdrawal tubing runsthrough withdrawal pump 142, and then into filter 150. Infusion tubing161 comes out the opposite end of the filter, travels through infusionpump 162, and then through the air detector. Blood traveling through thefilter, is treated by extraction of liquid, with the removed filtratemedia exiting the filter through the ultrafiltration line 176.Ultrafiltration media travels from the filter 150 through a blood leaksensor 172, and then ultrafiltrate pump 174. Ultrafiltration media iscollected in a reservoir 182 by the ultrafiltrate pump 174 pump itthough the tubing conduit 176. An optional weight scale 180 can beemployed to monitor the collection of ultrafiltrate media in thereservoir. Flow rates of the infusion pump and ultrafiltrate pumps arecontrolled by a pump console controller so that the sum of the infusionblood flow rate and the filtrate rate equals that of the withdrawal flowrate as determined by the withdrawal pump. Pressure sensors can helpmonitor this flow relationship.

Pumps 142, 162, and 174 are reversible blood and filtration pumps, suchas peristaltic roller pumps. The blood circuit is basically symmetricalabout the filter. In particular, the length of the tubing line from theimplanted port or catheter to the filter is equivalent to the lengthfrom the filter to the infusion catheter or implanted port. The firstblood pump 142 is connected to a first tube line 130 of the circuit, andthe second blood pump 162 is connected to the second tube line 132 ofthe circuit. The role of withdrawal and infusion is switched byreversing the rotational direction of the pumps. When the pumps arereversed the withdrawal access 112 is used for infusion and infusionaccess 118 is used for withdrawal.

Before treatment initiation, patient access is established for thevascular system. Patient access may be peripherally via standard IVneedle access or via implanted blood access port(s) or other such means.To initiate treatment, the ultrafiltration circuit is primed byconnecting the withdrawal connector 116 to a saline bag and the infusionconnector 122 to an ultrafiltrate reservoir 182 or some other fluidcollection device. The peristaltic roller pumps 142 and 162 operate in aclockwise direction until the tubing and filter are fully primed. Theair detector 134 senses that the tubing and filter have no air and arefully primed. When the circuit and filter are primed, theultrafiltration segment 176 can be primed by operating pump 174 in aclockwise direction while roller pumps 142 and 162 continue to operatein a clockwise direction. Priming of the access devices 112, 118 andextensions 114, 120 can be performed through connectors 116, 122 with asyringe or other appropriate method.

Blood pumps 142 and 162 are rotated at the same speed and in the samerotational direction while ensuring that pressure 160 is positive at alltimes. The pressure in the tubing may fall to a negative condition dueto a mismatch between pump flows that can be caused by for example thetolerances of the pump velocity settings, the tolerances of the tubingdiameter and other various tubing characteristics. If the pressuresensor 160 detects a negative pressure in the blood line while pumps 142and 162 are rotating clockwise, the controller may determine that thespeed of pump 162 is to be increased or decreased to maintain the bloodpressure in the circuit at a value or range of values such as 20 mmHg.The value(s) can in theory be any pressure positive or negative. Usingsuch a closed loop control system eliminates the need for impossiblytight tolerance requirements for the pumps and tubing segments

Once the circuit is primed, the patient is connected and treatmentinitiated. Since the blood circuit is symmetrical, pumps 142 and 162 canoperate in either a clockwise or counterclockwise direction. A userspecified blood flow rate will dictate how long operation can proceed inone direction before reversing. The length of time between pumpreversals is calculated such that, if a disconnection occurs, themaximum amount of blood which could be pumped and lost would preferablynot exceed a volume of 100 milliliters (ml), and may be set to notexceed a maximum blood loss in a range of 50 ml to 200 ml. Thecontroller may determine the blood volume passing through the circuitbased on the pump speed, and reverse the pump directions after thepredetermined maximum volume, e.g., 100 ml, has passed through thecircuit. After the calculated time has elapsed, pumps 142, 162 reversedirection. During clockwise rotation, the rotational rate of pump 162 isadjusted to match the rate difference of pumps 142 and 174. Thus:Q pump 142=Q pump 162+Q pump 174therefore Q pump 162=Q pump 142−Q pump 174

where Q pump 142 is the set blood pump flow rate, Q pump 174 is the setultrafiltrate flow rate and Q pump 162 is the difference between the setblood pump flow rate and the set ultrafiltrate flow rate.

During counterclockwise rotation, likewise the rate of pump 142 isadjusted by the controller to match the rotational rate difference ofpumps 162 and 174. Thus:Q pump 162=Q pump 142+Q pump 174 thereforeQ pump 142=Q pump 162−Q pump 174

Pump 174 operates in a clockwise rotation during normal ultrafiltrationmode. Ultrafiltration is controlled such that the filter removes a setfraction of fluid from the blood. The fraction is established tominimize any risk to the patient of excess blood concentration or toclot formation in the circuit. Pump 174 may operate in acounterclockwise rotation to backflush the filter or create some otherdesired pressure gradient across the filter. Since both infusion andwithdrawal blood lines travel through the air detector 134 beforereaching the patient, there is no risk of air entrainment reaching thepatient from the blood circuit.

Upon reversal of direction of pumps 142 and 162, the ultrafiltrationpump is temporarily stopped for a set period determined based on the setblood pump flow rate, circuit volume and access volume. During thisperiod the pump flow rates 142 and 162 are set to equal each otherbecause the ultrafiltrate pump 174 has been stopped. The filtrate isstopped to avoid circulating blood twice through the filter. A secondpass through the filter would further concentrate the blood and couldincrease the propensity of clots to form in the filter. The period offiltration cessation may be determined by dividing the summation of thehalf the volume of the extracorporeal circuit and the volume of blood inthe access path (collectively the flush volume) by the blood pump flowrate. Since this flush volume is a function of the access methodology,the operator enters the flush volume into the ultrafiltration device atthe time of setup.

Pressure sensors 140, 144, 160, 164, and 170 monitor the pressureswithin the circuit tubing throughout treatment to facilitate detectionof disconnects or occlusions. Pressure sensors can also be used tomonitor and verify pump flow rates and ultrafiltrate collection. Thepressure sensor 170 is used to ensure that the filter is not exposed toexcessively high TMP (Transmembrane Pressures). TMP may be calculatedas:TMP=((P144+P160)/2)−P170

Where P144 is pressure measured at pressure sensor 144, P160 is pressuremeasured at pressure sensor 160, and P170 is pressure measured atpressure sensor 170. Controlling the maximum negative pressure allowedat the pressure sensor site 170 ensures that the TMP does not becomeexcessively high. The ultrafiltrate rate is limited to set ultrafiltraterate. When the ultrafiltrate pressure 170 drops below a predefined setpressure limit, the ultrafiltrate rate is reduced to maintain the targetpressure using the pressure sensor 170 as feedback. This can also beused as a trigger to backflush the ultrafiltrate to clear filterfouling. For instance when the ultrafiltrate rate is less than 90% ofthe set ultrafiltrate rate for a 1 second period the ultrafiltrate pump174 is reversed. During this reversal it is necessary to increase theinfusion pump flow to accommodate the ultrafiltrate pump flow beingreturned. In the case of clockwise control this will result in the pump162 being increased to the set flow of Q pump 142+Q pump 174.

In addition to reversing pump direction to detect disconnects and bloodleaks, pump reversal can provide the benefit of clearing occlusionswithin the circuit and reducing the polarization layer which builds upwithin the filter fiber. Periodic pump reversals will reduce the chanceof occlusions occurring within the circuit and access devices byflushing them every other cycle. If occlusions are detected by thepressure sensor, a pump reversal can be initiated prior to the normalcycle reversal in an attempt to resolve the cause of the occlusion. Suchocclusions may occur due to vessel collapse, occlusion of cannulae tipor the formation of micro clots. Responding to them immediately willincrease the probability of resolving the issue.

FIG. 2 is a schematic diagram of another ultrafiltration device 200similar to the device 100 shown in FIG. 1 with the addition of ananticoagulant infusion system 203 and a position based ultrafiltratevolume limit detection system 220. Blood is withdrawn and infusedthrough blood lines 130 and 132. The blood is withdrawn through the airdetector 134 and through the filter 150 before being returned to thepatient and back through the air detector 134. To prevent clotting,heparin or other such anticoagulant is infused into the withdrawal line.When blood is withdrawn from a venous supply, the blood pressure in thewithdraw line will be negative and the pressure in the infusion linewill be positive. By using two one way valves 202 and 207, the infusedanticoagulant will always infuse into the withdrawal line obviating theneed for two anticoagulant pumps or some form of motor driven actuatorto switch the flow of anticoagulant when blood flow is reversed. It isgenerally accepted that it is better to infuse an anticoagulant upstreamof the filter because the filter is in the extracorporeal circuit andhas a high likelihood for initiating the clotting cascade. Infusing theanticoagulant upstream facilitates a high concentration of anticoagulantlocally within the circuit and filter while minimizing systemicanticoagulation.

When blood is withdrawn by pump 142 and infused by pump 162, thepressure at the anticoagulant T connector 201 is negative and positiveat T connector 206. The anticoagulation pump 304 is a syringe pump.Flows from syringe pumps are typically in the order of 0 to 20 ml/hrranging from drug delivery flow rates of 0 to 1000 units/hr when heparinis used as the anticoagulant in hemofiltration. Since thisultrafiltration device has considerably lower blood flows, a much lowerflow range of 0 to 2 ml/hr will suffice facilitating a much smallersyringe pump design. The syringe pump 304 delivers anticoagulant via theT connector 203 through two possible paths 208 or 209. When the pressureat T connector 201 is negative and T connector 206 positive the one wayvalve 202 is open and the one way valve 207 is closed and one way valve207 is open ensuring the anticoagulant is delivered upstream of thefilter. The T connector 203 is connected to the one way valve 202 via aconduit tube 209 and to one way valve 207 via a conduit tube 208. Oneway valve 203 is connected to T connector 201 via a conduit tube and oneway valve 207 is connected to T connector 206 via a conduit tube. Whenblood flow is reversed, the polarity of the pressures at T connectors201 and 206 will also be reversed resulting in one way valve 202 closingand one way valve 207 opening.

The ultrafiltrate removed from the filter 150 by the ultrafiltrate pump174 is withdrawn passed the blood leak detector 172 and pumped into thecollection reservoir 224 via the conduit tube 176. The blood leakdetector 172 uses a near infra red (IR) photo emitter and receiver witha peak sensitivity close to the isospectic point of blood, 820 nm. Inthe presence of ultrafiltrate and saline little or no attenuation of theIR signal occurs but in the presence of blood the IR signal is dispersedand greatly attenuated making it possible to measure the presence ofblood in ultrafiltrate. Blood in the ultrafiltrate indicates a breach ofthe filter membrane and when detected, causes the pumps to stop.

Because it is difficult to measure weight in an ambulatory system avolume expansion detection system is used which is independent ofweight. The reservoir bag is compressed by spring 226 and plate 223. Asthe ultrafiltrate is delivered to the reservoir, the reservoir expandsand the spring compresses. When the bag switch 221 arm 225 isintercepted by the spring plate 223 the switch is opened indicating thatthe bag is fully. The ultrafiltrate pump is stopped and the user isinformed via an alarm that the bag has to be emptied. The bag isdesigned to hold 250 ml. The switch 221 is connected electrically to thesystem processor via cable 222. The spring creates a maximum pressure intube 176 of 2 to 5 psi. This low maximum pressure is sufficient tocompress the bag while not presenting any significant resistive forcefor the peristaltic pump 174. Blood circuit peristaltic pumps have beendesigned to relieve at pressures exceeding 60 psi. A proximity switchmay also be used instead of a mechanical switch. The advantage of amechanical switch is that it consumes no energy. The reservoir 224 maybe emptied via the stopcock 240.

Ultrafiltration occurs inside the filter 150. Whole blood enters thebundle of hollow fibers from the cap of the filter canister. There areapproximately 160 hollow fibers in the bundle, and each fiber is afilter. Blood flows through a channel approximately 0.2 mm in diameterin each fiber. The fiber walls of the channel are made of a porousmaterial. The pores are permeable to water and small solutes butimpermeable to red blood cells, proteins and other blood components thatare larger than 50,000-60,000 Daltons. Blood flow in fibers istangential to the surface of the filter membrane. The shear rateresulting from the blood velocity is high enough such that the pores inthe membrane are protected from fouling by particles, allowing thefiltrate to permeate the fiber wall. Filtrate (ultrafiltrate) leaves thefiber bundle and is collected in a space between the inner wall of thefilter canister and outer walls of the fibers.

The geometry of the filter is optimized to prevent clotting and foulingof the membrane. The active area of the filter membrane is approximately0.023 m². The permeability KUF of the membrane is 30 to 33mL/hour/m²/mmHg. These parameters allow the desired ultrafiltration rateof approximately 1 liter to 3 liters every 24 hrs at the TMP of 150 to250 mmHg that is generated by the resistance to flow. The effectivefilter length is 22.5 cm and the diameter of the filter fiber bundle is0.5 cm. The blood shear rate in the filter may be 850 to 2500 sec-1 atblood flow rate of 5 to 15 mL/min.

Since the device is to be ambulatory the return 132 and withdrawal 130tubing may be 60 cm in length. With a tubing diameter of 2.5 mm thevolume in the complete circuit blood path is less than 7 mL. With atubing diameter of 2 mm the volume in the complete circuit blood path isless than 5 mL. Minimizing this volume reduces the blood residence timeof the devices propensity to clot.

FIG. 3 shows a diagram of the apparatus worn by a patient as describedin FIG. 2. The ultrafiltration device may be attached to a waist beltworn by the patient 300 or over the shoulder or on the back of thepatient to provide ambulatory use of the device. Access to the patientblood is depicted by 301 via an implanted port with its cannulae placedcentrally. Withdrawal and infusion blood lines 132 and 130 exit from thepatient access site 301 and are connected to the ultrafiltration device304 and 303 at the back of the patient. The console 304 includes aliquid crystal display (LCD) 305 and a membrane panel for viewing andentering patient therapy parameters. The reservoir 308 is separate fromthe console and is connected to the console via the electrical cable 309and the ultrafiltrate conduit tube 176. Keeping the reservoir separateminimizes weight accumulation on a specific area and also reduces thehazard of wetting the console. Additional battery packs may also bestored on the belt and may be connected directly to the ultrafiltratedevice as needed. When the reservoir is full the console annunciates analarm requesting the user to empty the ultrafiltrate reservoir. Areservoir may be disconnected and emptied or drained using an extensionhose connected to the reservoir minimizing the potential for spill onthe patients clothing.

FIG. 4 shows a detailed view of the cantilevered pressure transducerassembly 400 used for measuring pressures at sites 140, 144, 160, 164and 172 shown in FIG. 2. The user inserts the tubing into the recessdefined by the lever arm strain gauge 401 and the housing body 402. Thelever arm strain gauge 401 is attached to the housing by a securingscrew 301. The circuit tubing 403 which is normally cylindrical in shapeis deformed to an oval shape by the insertion of the tube into thepressure transducer recess defined by 401 and 402. The lever arms 401central axis 404 is depicted in FIG. 4 when atmospheric pressure ispresent within the circuit tube and when a positive pressure 405 ispresent within the tube. The lever arm 401 is bent upwards such that thecentral axis 405 when pressure is positive and bent downwards whenpressure is negative. The strain gauge consists of a Wheatstone bridgeresistor network on the lever arm and changes in resistance inproportion to the pressure exerted by the circuit tube. This isinterpreted as an electrical signal when the transducer is excitedelectrically via 2 excitation wires of the 4 wire electrical cable 406.

Since the ultrafiltration device does not need pressure sensors for thedetection of disconnects, a similar approach to that used to measurepressure used by standard infusion pumps may be employed. The expansionof the blood lines is used to monitor for the detection of occlusions byuse of force gauges which convert the force exerted by the blood andultrafiltrate tubing to an electrical signal. The force gauge may be aload cell similar to that sold by SMD (Strain Measurement Devices) ofMeriden, Conn. and St. Edmunds, England.

The load cell may include a lever arm that applies pressure to thetubing by compressing it slightly. At the start of the treatment themeasured pressure can be zeroed mathematically by the pump consolemicroprocessor to remove offsets due to tubing position. When underpositive pressure the tube expands against the load cell lever armraising the lever arm producing an electrical signal proportional to thepressure in the tube. When under negative pressure, the tube collapsesand thereby lowers the lever arm create an electrical signalproportional to the pressure in the tube. These electrical signals maybe read by an analog to digital converter and translated to pressuremeasurements via a transfer function. Unfortunately, such pressuresensors implementations are notoriously bad for variances in offsetsbecause of the creep characteristics of polymers. It is possible tochoose polymers that minimize creep but this is a medical applicationand the numbers of materials that are biocompatible, have low creepproperties and facilitate peristaltic action provides a significantdesign challenge. Peristaltic pump tubing requires that the tubing beflexible and compliant, i.e. of low durometer, otherwise the torquerequired to compress the tubing is excessive. It is possible to usedifferent materials for each section of the circuit but this will createadditional joints decreasing the reliability of the blood circuit. It isdifficult to reliably bond different polymers materials to each otherand such a construction creates an added hazard for disconnects andleaks. It is also helpful to minimize the number of transitions andjoints in the circuit be minimized to decrease the circuits clottingpropensity and improve circuit reliability.

FIG. 5 shows a diagram of the electrical architecture of theultrafiltration device consisting of the console 305 and reservoir 308.The console 304 houses the LCD 305, membrane panel 306, blood leakdetector 172, pressure sensors 140, 144, 170, 160 and 164, battery pack506, blood pumps 142 and 162, ultrafiltrate pump 174, syringe pump 508,alarm speaker 508 and main printed circuit board (PCB) 502. Within themain PC 502 there are 3 processors, the main central processor (CP) 503,the pump motor control (MC) CP 504 and the safety CP 505. Each of thesensor readings including blood leak, air detector, pump encoders andpressure sensors are shared between the main CP and the safety CPfacilitating a control and monitor implementation for system safety. Thepumps motors are each driven by a brushless DC motor and electricallycommutated by the MC CP using encoder feedback and ½ bridge circuit onthe PCB 502. Each motor has a quadrature encoder which outputs A and Bquadrature digital signals as the motor is rotated as a function ofmotor position. Each motor is geared for optimal efficiency with a gearratio of 10:1 resulting in a peak power consumption of less than 2 wattsper motor. In order to conserve energy the pressure sensors, blood leakdetector and air detector are only powered when it is necessary to readthe sensor signal. This reduces the power consumption of these devicesby a factor of 10. The digital sample rate for the console sensors is 50Hz. The console battery pack operates at 12 VDC and uses NiMH chemistry.Charging of the batteries is performed off line with a separate batterycharger. This reduces the electrical circuitry required during operationand minimizes power consumption and space requirements. Use of anexternal power source is possible via and external power supply with anoutput of 12 VDC. The battery supply is disabled when an external powersupply is connected.

The reservoir 308 is connected electrically via a 2 wire cable to theconsole 304 providing electrical connection for the reservoirs expansionlimit mechanical switch 221. The mechanical switch 221 is normallyclosed until the reservoir is full. When full the switch is thrown openproviding the additional safety that if the electrical cable were tobecome disconnected ultrafiltration would be stopped.

The main CP reads each of the pressure inputs and updates the blood andultrafiltrate pumps velocity every 20 ms. The liquid crystal display(LCD) is only powered if it has a message to display or if the operatorpresses a membrane panel key. The console duty cycles a green lightemitting diode (LED) every second to indicate that it is operatingcorrectly. In the event of a problem, a red LED is flashed and an alarmannunciated via the speaker. The LCD is then powered on and displays amessage informing the users of the potential cause of the issue andremedy.

FIG. 6 shows a flow chart of which pressure sensors the ultrafiltrationdevice uses for feedback when in clockwise or anticlockwise blood pumprotation and which pumps it uses to control these pressures to limitpressure excursions. Four pressure control loops are operatingsimultaneously. These loops are: (i) the withdrawal pressure controlalgorithm, (ii) the infusion pressure control algorithm, (iii) thefilter positive pressure control algorithm and (iv) the ultrafiltratepressure control algorithm

In flow chart 600 the terms Pxfeedback and Qxcontrol are used where Pdenotes pressure, Q flow of pump, x the control algorithm i.e. wwithdrawal, i infusion, c filter pressure or center pressure and uultrafiltrate.

During blood pump reversals of pumps 142 and 162 from anticlockwiserotation to clockwise rotation the pressure transducers used forfeedback are changed in conjunction with the blood pumps used forcontrol. During clock wise rotation 620, the pressures within the filterare kept slightly positive by using the pressure sensor 160 as feedbackand the blood pump 162 as control as shown in block 610. This is alsotrue in the event of a withdrawal occlusion because the pressure sensor140 is used as feedback and the blood pump 142 is used as the controlblood pump as shown in block 608. No conflict arises between two controlloops trying to control the same pressure. But in the case of aninfusion occlusion when the blood pumps are rotating clockwise thepressure sensor 164 is used as feedback and the blood pump 162 is usedas control as shown in block 609.

To maintain positive pressure within the filter the same feedbackpressure sensor 160 is used as shown in blocks 610 and 611 but thecontrol pump is changed from 162 to 142. This eliminates any conflictbetween which pump is used for control while still maintaining bothpressure targets. The withdrawal and infusion pressure targets read bypressure sensors 140 and 160 respectively are −300 and 300 mmHgrespectively. The blood pump flows are limited by the user defined setblood pump flow which is set to be as high as possible based upon theavailable access minimizing blood circuit residence time and maximizingthe maximum rates of ultrafiltration. The maximum extraction rate ofultrafiltrate is limited to 21% of blood flow. If an infusion occlusionis persistent for an extended period of time then the direction of theblood pumps are reversed. Blood pump reversals are normally timed basedand are a function of set blood pump flow but in the vent of apersistent occlusion in either the withdrawal or infusion line thereversal sequence may be initiated early.

During blood pump reversals of pumps 142 and 162 from clockwise rotationto anticlockwise rotation the pressure transducers used for feedback arechanged in conjunction with the blood pumps used for control. Duringanticlockwise rotation 621 the pressures within the filter are keptslightly positive by using the pressure sensor 144 as feedback and theblood pump 142 as control as shown in block 605. This is also true inthe event of a withdrawal occlusion because the pressure sensor 164 isused as feedback and blood pump the blood pump 162 is used as thecontrol blood pump as shown in block 608. No conflict arises between twocontrol loops trying to control the same pressure. But in the case of aninfusion occlusion when the blood pumps are rotating anticlockwise thepressure sensor 140 is used as feedback and the blood pump 142 is usedas control as shown in block 604. In order to maintain positive pressurewithin the filter the same feedback pressure sensor 144 is used as shownin blocks 605 and 606 but the control pump is changed from 142 to 162.This eliminates any conflict between which pump is used for controlwhile still maintaining both pressure targets.

During both clockwise and anticlockwise blood pump rotation theultrafiltrate pressure is limited to a maximum negative pressure of −300mmHg., for example. Block 612 shows that the pressure sensor 174 andultrafiltrate pump 174 are unaffected by blood pump direction.

FIG. 7 shows how the pressure control loop 700 is implemented. Thispressure control loop is used for all four control loop described inFIG. 6. The difference between the target pressure 700 and the feedbackpressure 705, the pressure error are input to a PI (ProportionalIntegral) control loop 703. Each time there is a setting change to theblood flow, UF rate or the ultrafiltrate pump has to be reversed as partof a back flush maneuver the feed forward term (FF) 706 is updated todifference between the set blood flow and the UF rate. Thus in the caseof clockwise control the FF term 706 is set to:FF=Q pump 162=Q pump 142−Q pump 174

Upon initiation of the control loop the integration term of the PI loopis set to 0 ml and is limited to +/−20% of the set blood flow rate toprevent windup of the integrator. Thus if the blood flow is set to 10ml/min the maximum the integration term if allowed to sum to is +/−1ml/min when trying to the pressure sensor 160 to the target pressureP_(target). The +/−20% limit is chosen because the blood pump has anaccuracy of +/−10% and variations significantly above of below thisimply a fault condition.

The resultant pump flow of the summed PI output and the FF term iscommanded by the MC CP to the pump 703 which delivers the desired fluidflow and results in a circuit 704 causing the pressure 705 due to thecircuit and access resistance. This pressure 705 is read by the Main CPusing an ADC (Analog to Digital Convertor) and is used to calculate thepressure error by subtracting the feedback pressure 705 from the targetpressure 701.

FIGS. 8 a to 8 k are diagrams depicting the air detector andcross-sections of the withdrawal and return tube passing through the airdetector. The dual lumen tube design eliminates the need for a secondair detector and also reduces the power consumption requirements for thedevice. This minimizes the required space, weight and battery capacityfor device operation.

The air detector 801 uses an ultrasonic emitter 802 and receiver 803.The withdrawal and return tubes 804 are inserted into the air detectorslot and as long as the lumens are full of liquid no air detection willbe detected. If a bubble of gas is entrained into the withdrawal ofreturn tube, passes through the air detector and is greater than 50microliters in volume, an air detected alarm is annunciated by theconsole. The signal strength received by the receiver will dramaticallyreduce in the presence of an air bubble because a gas is significantlyless dense than a liquid and there are large losses in the energy beingtransmitted making the detection of bubbles possible. This will beinterpreted as an air detected alarm by the ultrafiltration device.Testing has shown that it is possible to insert two single circularsingle lumen tubes into a standard air detector and to detector air ineither lumen. It is difficult to place such single lumens into the airdetector slot and a better alternative is to extrude the two lumenstogether. FIGS. 8 b to 8 k show the many combinations of tubingcross-section supporting dual, triple and multiple lumens which willsupport such an air detection implementation. The patient circuit tubingis inserted into the air detector slot during the priming sequence ofthe ultrafiltration device.

FIG. 8 b shows a dual oval shaped co-extruded cross-section. It wouldalso possible to make such a portion of tubing by gluing two tubestogether to facilitate. FIGS. 8 c and 8 d show an hour glass dualcircular co-extruded cross-section in both the horizontal and verticalposition demonstrating orientation is not important when inserting thetubing segment into the air detector for the purposes of detecting air.Such a cross-section could be extruded or be formed from gluing twotubes together as part of the circuit manufacturing process. Eitherextruding or gluing will enable a similar cross-section. Thecross-section of the two lumen tubing is also not limited to being hourglass shaped, it may be square in shape as shown in FIG. 8 e or circularwith two inner D lumen as shown in FIG. 8 f or a combination of twolumen shapes ranging from circular and oval to kidney shaped as shown inFIG. 8 g. FIG. 8 h shows a co-extruded concentric tubing cross-sectionwhich will also work. Air in either channel will result in an airdetection alarm. FIG. 8 k shows a double oval lumen implementation of adual lumen tubing implementation. The purpose of showing theseconfigurations is to demonstrate that the implementation is not limitedto a specific tubular configuration and that many implementations arefeasible.

This air detection scheme will also work for multiple lumens. FIG. 8 ishows a three lumen implementation using a square profile. FIG. 8 jshows a similar three lumen implementation using a circular lumenprofile. The detection method will work with multiple lumens as shown inFIGS. 8 b to 8 k.

The invention has been described in connection with what is presentlyconsidered to be the most practical and preferred embodiments. Theinvention is not to be limited to the disclosed embodiments, but, on thecontrary, covers various modifications and equivalent arrangementsincluded within the spirit and scope of the appended claims.

What is claimed is:
 1. An extracorporeal blood treatment systemcomprising: a blood circuit comprising a first blood passage coupled toa blood filter and a second blood passage coupled to the blood filter,wherein said first and second blood passages each are adapted to becoupled to a vascular system of a human patient; at least one blood pumpconnectable to the first blood passage, wherein said pump is adapted tomove blood through the first and second blood passages and the filter, afiltrate collection container configured to receive filtrate withdrawnfrom the filter, a single air-in-blood detector configured tosimultaneously monitor both the first and second blood passages, a pumpcontroller operatively connected to the blood pump to control a rate ofblood withdrawal into the blood circuit wherein the single air-in-blooddetector comprises a housing including a slot configured to receive twoor more passages configured as flow passages for extracorporeal blood; atransmitter of wave energy in the housing and oriented to direct waveenergy across the slot and through the two or more passages, and areceiver of wave energy in the housing and oriented to receive waveenergy transmitted by the transmitter, and the receiver configured togenerate a signal indicative of the received wave energy passing throughthe two or more passages.
 2. An extracorporeal blood treatment system asin claim 1 wherein said system further comprises a harness wearable bythe patient and said harness supports the blood pump, filter, pumpcontroller and filtrate collection container.
 3. An extracorporeal bloodtreatment system as in claim 1 wherein the pump periodically reverses ablood flow direction through the passages.
 4. An extracorporeal bloodtreatment system as in claim 1 wherein the pump periodically reversesthe blood flow direction after a volume of blood flow through thecircuit is no greater than 200 ml.
 5. An extracorporeal blood treatmentsystem as in claim 1 wherein the wave energy is ultrasonic energy, thetransmitter is an ultrasonic transmitter and the receiver is anultrasonic receiver.